NetNews Offline 2/NetNews Offline Volume 2.iso/news/comp/lang/c++-part1/9590

Internet Message Format | 1996-08-05 | 1.7 KB

Path: rain.fr!world-net!usenet
From: Frederic LACHASSE <[e-mail]>
Newsgroups: comp.lang.c++,rb.technical
Subject: Re: Can copy constructor and operator= share code?
Date: Sat, 02 Mar 1996 23:18:20 +0000
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Message-ID: <VA.00000053.00cdab05@fred>
References: <4h2kcn$[e-mail]>
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In article <4h2kcn$[e-mail]>, [e-mail]
(Boris Burtin) wrote:
>
> I have noticed that a copy constructor and operator= perform pretty
> much the same function.  The code I wrote for my class simply copies
> each member variable from one class to the other.
>
> Is there a way for the one of the two functions to call the other, to
> avoid duplicate code?  I have tried calling the copy constructor from
> operator=, but nothing happens.  I've gotten around this problem by
> creating a private Copy() function, which is called by both the copy
> constructor and operator=.  Is there another way?
>

Generally, the operator=() must release old resource and create a copy
of the other object. So a generic operator=() can be:

T &T::operator =(const T &t)
{
  if (this != &t) // if objects are same, nothing to do
  {
    ~T(); // explicit call to destructor to release resources.
    new(this) T(t); // use of the placement operator to call the
                    // copy constructor.
  }
}

Some times though, the assignement operator can be optimize to reuse
resources of the old object.

 Frederic LACHASSE (ECP 86)
 CompuServe: 100530,2005
 Internet: [e-mail]